In a 4-cycle, 4-cylinder internal combustion engine for a vehicle, a secondary inertia force occurs at a center of gravity of a piston-connecting rod system in terms of its layout.
As means for setting off or balancing the secondary inertia force, the engine has a balancer apparatus for rotating a balancer shaft at a speed that is twice as fast as engine rotational speed.
JP-A-2003-113898 discloses a mounting method for a balancer apparatus that includes integrally assembling the balancer apparatus with a cylinder block or attaching the balancer apparatus to either a lower crank casing or to an oil pan located just under a crank shaft.
In the case of the mounting method of attaching the balancer apparatus to the lower crank casing or to the oil pan just under the crank shaft, in order to realize a compact size, there is a layout in which the balancer apparatus and an oil pump are integrated.
Generally, in such a layout a pump rotor of the oil pump rotates coaxially with the balancer shaft and it is necessary to rotate the pump rotor at a speed which is twice as fast as the engine rotational speed. Therefore, it is necessary to construct an inlet passage and a delivery passage as oil passages located before and after the pump rotor to provide an oil flow that is as smooth as possible.
Hitherto, in the balancer apparatus for an internal combustion engine disclosed in JP-A-2003-129816, a receiving portion of a relief valve for adjusting a discharge pressure of the oil pump is integrally provided with the housing and the relief valve is arranged at a position away from an extension of the inlet passage, thereby simplifying oil passage construction and realizing a compact size for the entire apparatus.
In the housing of the balancer apparatus for the engine, an attaching portion of an oil strainer is integrally formed at a lower position of the balancer shaft on the lower side between the two balancer shafts, thereby miniaturizing the apparatus.
Hitherto when the balancer apparatus and the oil pump are integrally arranged to realize the compact size, it is difficult to smoothly construct the oil inlet passage and the oil delivery passage located before and after the pump rotor, respectively. This problem causes discharge performance of the oil pump to deteriorate and drive loss of the oil pump to increase.
In the case of the transverse front positioned engine/front-wheel drive (FF) engine, it is desirable that the oil strainer is arranged in front of the vehicle so as to avoid air suction during vehicle deceleration. In this case, however, the oil passage to the oil strainer becomes too long and thus mountability of the balancer apparatus to the engine deteriorates.
Therefore, an object of the invention is to provide a balancer apparatus for an engine, such as an internal combustion engine, in which discharge performance of an oil pump and mountability to the engine are improved.